As natural gas wells mature, gas production decreases due to a decline in reservoir pressure. The formation fluids (i.e., water and liquid hydrocarbon condensate), which result from high production rates, can no longer be lifted from the well and accumulate in the well bore. This accumulation may cause the well to flow erratically at a much lower flow rate and eventually cease production. Foaming agents, also known as foamers, are one of the many methods available to de-water a gas well. Foamers can be applied either by batch treatment or continuous application. With the addition of foamer to the wellbore where the loading liquids are present, foam is generated with agitation from the gas flow. The surface tension and fluid density of the foam are much lower than the liquids so the lighter foam, where the bubble film holds the liquids, is more easily lifted by the low gas flow rate. In oil well production, foamers are also used in conjunction with a gas lift system to enhance oil recovery.
A lot of attention and effort have been attracted to recover coal seam gas (CSG) for use as natural gas fuel in recent times due to high energy demand. As a consequence of this type of production, there is a large volume of produced water, which is commonly cleaned and purified by using reverse osmosis (RO) membrane filtration units. This enables the diverse re-use of the water and offers a sustainable production approach, especially in countries such as Australia, where water is always in high demand. However, the membrane cleaning processes can only be applied for produced water which does not contain components blocking or fouling the membrane. The treated water can be reused for applications such as agriculture and municipal purposes. Typical foamers employed to accelerate the water unloading and maintain the integrity of the asset can generally destroy or block the RO membranes.
Currently available foamer technologies that are incompatible with the RO membranes include the following. WO 2009/064719 discloses imidazoline-based heterocyclic foamers for gas/oil well deliquification, but such quaternary compounds are not compatible with the RO membranes. U.S. 2006/0128990 teaches a method of treating a gas well applying a chloride free amphoteric surfactant. U.S. Pat. No. 7,122,509 provides a method of preparing a foamer composition having an anionic surfactant and a neutralizing amine. In U.S. 2005/0137114, an aqueous foaming composition comprising at least one anionic surfactant, cationic surfactant and at least one zwitterionic compound is disclosed. WO 02/092963 and U.S. 2007/0079963 disclose methods for recovering oil from a gas-lifted oil well using a lift gas and a foaming surfactant which consists of nonionic surfactants, anionic surfactants, betaines, and siloxanes.
While the discussed foamers contribute significantly to deliquifying solutions, there is still need for other cost-effective foamers which could provide superior foaming performance and are membrane compatible.